Ultrasonic delay line

ABSTRACT

A thin flat ultrasonic delay line comprising a solid glass body in the shape of a parallelepiped with pentagonal top and bottom boundary surfaces extending perpendicular to the thickness dimension of the body and substantially parallel to the desired propagation path in the body for the ultrasonic wave energy. An input and an output transducer are mounted on first and second side surfaces of the body that extend perpendicular to said boundary surfaces. The body thickness is less than five times the wavelength of the wave energy. The transducers are polarized parallel to both the boundary surfaces and the first and second contact surfaces. Parts of the aforesaid boundary surfaces outside of the desired energy propagation path are arranged to attenuate wave energy impinging thereon.

United States Patent [72] inventors Theodorus Bartholomeus AntoniusMaria Sliepenbeelt; Manfred Franz Kari Gm'nmel, both of Emmasingel,Eindhoven, Netherlands [21] Appl. No. 872,913 [22] Filed Oct. 31, 1969[45] Patented Oct. 5, 1971 [73] Assignee US. Philips Corporation NewYon-lit, NY. [32] Priority Nov. 9, 1968 3 3 Netherlands [31 l 681 6005[54] ULTRASONIC DELAY LiNE 6 Ciaims, 2 Drawing Figs.

[52] ILLS. Cl 333/30 [51] int. C1 110311 9/30 [501 Fieid 01 Search333/30 M, 30, 71

[5 6] References Cited UNITED STATES PATENTS 3,173,100 3/1965 White333/30X 3,307,120 2/1967 Denton et a1. 333/30 Primary ExaminerHermanKarl Saalbach Assistant Examiner-Saxfield Chatson, ilr. Attorney-FrankR. Trifari ABSTRACT: A thin flat ultrasonic delay line comprising asolid glass body in the shape of a parallelepiped with pentagonal topand bottom boundary surfaces extending perpendicular to the thicknessdimension of the body and substantially parallel to the desiredpropagation path in the body for the ultrasonic wave energy. An inputand an output transducer are mounted on first and second side surfacesof the body that extend perpendicular to said boundary surfaces. Thebody thickness is less than five times the wavelength of the waveenergy. The transducers are polarized parallel to both the boundarysurfaces and the first and second contact surfaces. Parts of theaforesaid boundary surfaces outside of the desired energy propagationpath are arranged to attenuate wave energy impinging thereon.

PATENTEDHBI 5m 3,611,200

1| III INVENTORS THEODORUS 8. AM. SLIEPENBEEK MANFRED F. .GAMMEL iwwa zULTRASONIC DELAY LINE The present invention relates to an ultrasonicdelay line comprising a solid body on which are provided one or moretransducers for converting electrical energy into ultrasonic mechanicalvibration energy, and vice versa, part of the body outside of thedesired propagation path of the ultrasonic wave being designed as areasof attenuation for this wave. Generally, the material of the body isglass or another substance of slight temperature dependence so that thetime interval between the reception of an electric input signal and thetransmission of a corresponding electric output signal, during whichtime interval the input signal is converted into a mechanical vibrationwhich in turn is reconverted into an electric signal, is virtuallyindependent of the temperature. As a rule, the solid body is madecomparatively thick in order to ensure that it has sufficient mechanicalstrength and to enable the contact surfaces for the provision of thetransducers to be of sufficient size.

According to recent developments it has proved possible tosimultaneously manufacture a large number of ultrasonic delay lines bystarting from, for example, a prismatic glass body on one or two sidesof which transducers are provided. Another side of the glass body isground flat to enable it to serve as a reflecting surface for themechanical vibration. The body is subsequently cut into thin slices bysawcuts extending at right angles to the said sides. The resulting partscan each be used as an ultrasonic delay line.

According to the invention this method of manufacturing ultrasonic delaylines permits of cheap large-scale manufacture, for which, however,several additional conditions have to be satisfied. The invention ischaracterized in that the body has a thickness which is less than fivetimes the wavelength of the mechanical vibration, that the transducersare polarized in a direction parallel to the boundary surfaces of thebody which extend at right angles to the direction of thickness, and ina direction parallel to their surfaces of contact with the solid, whichsurfaces are at right angles to the said boundary surfaces, and thatsuitably selected portions of these boundary surfaces which consequentlyextend substantially parallel to the direction of propagation of theultrasonic wave propagating through the body, are designed as the saidareas of attenuation for this wave.

The invention is based on the discovery that by described choice of thedirection of polarization of the transducers, the said boundary surfacesact as mirrors for the ultrasonic vibration and hence give rise tocomparatively little damping. However, owing to the natural spreading ofthe ultrasonic wave, for example, by diffraction phenomena, withoutfurther expedients it will be extremely difficult to obtain a reliablyoperating delay line since various undesirable reflections may occur. Inaddition, the ultrasonic wave may follow various undesirable paths sothat no exactly defined delay time is obtained. It is known to providedamping material at the undesirable reflecting faces for the ultrasonicwave outside the desired path of this wave so that the wave isconstrained within the desired path. Furthermore it has been proposed toattenuate the undesirable stray radiation by roughening the wall bymeans of a grinding or etching process, or to press corrugations in thedelay-line body during the moulding process of the hot and still ductileglass. lf, now, according to a further discovery on which the inventionis based, the thickness of the body is made smaller than five times thewavelength, it will be possible, although the said boundary surfacesextend substantially parallel to the direction of propagation of theultrasonic wave, either to provide on the said boundary surfacesmaterial which damps the ultrasonic wave or attenuates it in anothermanner or, for example, to etch parts of these boundary surfaces so asto ensure effective attenuation of the undesirable ultrasonic wavepassing these parts. lf the body thickness is made greater this mannerof damping is insufficiently effective. in practice, a thickness of, forexample, 1 mm. is chosen. A smaller thickness also is permissible solong as sufficient mechanical strength is provided. For color televisionreceivers in which a delay time of 64 us is desired, the wavelength isabout 0.6 mm. Thus the thickness is smaller than twice the wavelength.The invention will be described more fully with reference to theaccompanying drawing, in which:

FIG. 1 is a plan view of an ultrasonic delay line according to theinvention, and

FIG. 2 is a side elevation thereof.

The delay line shown in Fig. l comprises a body ll composed of asuitably chosen material, for example, glass. The body 1 has the shapeof a parallelopipedum with pentagonal base having parallel sides 2 and3, a side 4 at right angles thereto and sides 5 and 6 at angles of aboutC. to the sides 2 and 3 Transducers 7 and 8 are provided on sides 5 and6, respectively, so that the mechanical vibration produced by thetransducer 7 is successively reflected at the faces 2, 3, 4, 2 and 3before striking the transducer 8. The thickness d of the body l is madesmaller than five times, preferably smaller than twice, the wavelengthof the ultrasonic mechanical vibration. The transducers 7 and 8 arepolarized parallel to their surfaces 5 and 6 of contact with the body 1,respectively, and also parallel to the upper and lower boundary surfaces9 and 10, respectively, of the body l, which latter surfaces maybeformed by cutting the body from a larger body of glass. Further,damping material 1111, for example, silicone rubber, is provided in theform of a layer 1% mm. thick on the surfaces 9 and/or 10 in the areasshown by hatching in Fig. l. The said choice of the direction ofpolarization ensures that the surfaces 9 and 110, which in themselveshave little damping power, act as mirrors for the ultrasonic mechanicalvibration owing to the small thickness d used, so that the dampingmaterial lll effectively contributes to the fact that the ultrasonicwave emitted by the transducer 7 is compelled to follow the path showntowards the transducer 3. As a result, undesirable stray radiation andconsequent undesirable blurring of the delay time to be produced areavoided.

What is claimed is:

ll. An ultrasonic delay line comprising, a solid body for transmittingultrasonic wave energy along a desired path in the body, one or moretransducers in contact with the body for converting electrical energyinto ultrasonic mechanical vibration energy and vice versa, said bodycomprising first and second boundary surfaces which extend at rightangles to the thickness dimension and substantially parallel to thedesired direction of propagation of the ultrasonic wave in the body,said thickness dimension of the body being less than five times thewavelength of the mechanical vibration, said transducers being polarizedparallel to the first and second boundary surfaces of the body and alsoparallel to their surfaces of contact with the body, said contactsurfaces being at right angles to said boundary surfaces, and waveenergy attenuation means located on suitably chosen parts of theboundary surfaces that lie outside of the desired path of the ultrasonicwave thereby to attenuate wave energy impinging thereon.

7. An ultrasonic delay device comprising a thin flat solid body fortransmitting ultrasonic wave energy along a desired propagation pathwithin the body, said body comprising first and second boundary surfacesextending normal to the thickness dimension of the body andsubstantially parallel to said desired energy propagation path and thirdand fourth side surfaces which extend normal to said boundary surfaces,said thickness dimension being less than five times the wavelength ofthe ultrasonic wave energy, an electromechanical input transducer incontact with said third surface and an electromechanical outputtransducer in contact with the fourth surface, said transducers beingpolarized parallel to the boundary surfaces and parallel to theirrespective contact surfaces. and wave energy attenuation means locatedon at least one of said boundary surfaces at given areas that lieoutside of the desired energy propagation path thereby to effectivelyconfine the wave energy to said desired path by dissipating the waveenergy impinging thereon.

3. A delay device as claimed in claim 2 wherein said given areas of theboundary surface are roughened to constitute said wave energyattenuation means.

the seventh surface.

6. A delay device as claimed in claim 2 wherein said thickness dimensionis chosen to be less than twice the wavelength of the ultrasonic waveenergy.

1. An ultrasonic delay line comprising a solid body for transmittingultrasonic wave energy along a desired path in the body, one or moretransducers in contact with the body for converting electrical energyinto ultrasonic mechanical vibration energy and vice versa, said bodycomprising first and second boundary surfaces which extend at rightangles to the thickness dimension and substantially parallel to thedesired direction of propagation of the ultrasonic wave in the body,said thickness dimension of the body being less than five times thewavelength of the mechanical vibration, said transducers being polarizedparallel to the first and second boundary surfaces of the body and alsoparallel to their surfaces of contact with the body, said contactsurfaces being at right angles to said boundary surfaces, and waveenergy attenuation means located on suitably chosen parts of theboundary surfaces that lie outside of the desired path of the ultrasonicwave thereby to attenuate wave energy impinging thereon.
 3. A delaydevice as claimed in claim 2 wherein said given areas of the boundarysurface are roughened to constitute said wave energy attenuation means.4. A delay device as claimed in claim 2 wherein said body furthercomprises fifth, sixth, and seventh side surfaces arranged normal tosaid boundary surfaces to reflect wave energy propagating along thedesired path.
 5. A delay device as claimed in claim 4 wherein said fifthand sixth surfaces are approximately parallel and normal to the seventhsurface.
 6. A delay device as claimed in claim 2 wherein said thicknessdimension is chosen to be less than twice the wave-length of theultrasonic wave energy.
 7. An ultrasonic delay device comprising a thinflat solid body for transmitting ultrasonic wave energy along a desiredpropagation path within the body, said body comprising first and secondboundary surfaces extending normal to the thickness dimension of thebody and substantially parallel to said desired energy propagation pathand third and fourth side surfaces which extend normal to said boundarysurfaces, said thickness dimension being less than five times thewavelength of the ultrasonic wave energy, an electromechanical inputtransducer in contact with said third surface and an electromechanicaloutput transducer in contact with the fourth surface, said transducersbeing polarized parallel to the boundary surfaces and parallel to theirrespective contact surfaces, and wave energy attenuation means locatedon at least one of said boundary surfaces at given areas that lieoutside of the desired energy propagation path thereby to effectivelyconfine the wave energy to said desired path by dissipating the waveenergy impinging thereon.